This invention relates to a two-cycle internal combustion engine.
In a conventional two-cycle engine of the crank chamber pre-compressing type, scavenging paths extend along the inner wall of the cylinder as well as into the crankcase, the upper ends of the scavenging paths serving as scavenging ports which are opened and closed through reciprocating movement of the piston. Openings are provided in the peripheral wall of the piston at positions near the piston-pin bosses thereof in such a manner as to allow them to normally communicate with the scavenging paths during scavenging, air-fuel mixture being conveyed to the scavenging ports by way of the outer route through the scavenging paths and the inner route extending through the inner space of the piston. In a conventional engine with the above construction, the openings provided in the peripheral surface of the piston are formed as relatively large openings which are symmetrically arranged with respect to the piston-pin bosses, i.e., one on the side of the suction inlet and the other on the side of the exhaust outlet. Because of this, the flow which occurs within the piston during scavenging stroke is rather weak, so that a back flow running backward to the scavenging flow, i.e., a pulsating flow is likely to be generated therein. This is especially the case during a low-speed operation such as idling. Such a pulsating flow may be the cause of irregular combustion, resulting in variations in the rotational speed of the engine, insufficient cooling of the piston, etc.